1. Field of the Invention.
This invention relates to a DC voltage powered, rotating brush type motor that has particular application for use in an electric vehicle and is characterized by a high power-to-weight ratio. The motor includes a pair of brush assemblies that rotate relative to a stationary double sided commutator assembly and a pair of slip ring assemblies.
2. Background Art.
Conventional brushless motors are known to have electronic commutation control means that require as many as six semiconductor transistor devices. In this case, the commutator is commonly mounted on and rotatable with the shaft of the motor. The magnetic structure of the motor is part of the stationary stator assembly. In cases where the motor has current conducting brushes, such brushes are typically stationary within the motor housing relative to a rotating commutator assembly. Current from the brushes is carried via shunt wires through relatively long current paths to the field windings which increases impedance and reduces the current carrying capacity of the motor.
The conventional brushless and stationary brush type motors tend to generate excessive heat that requires cooling and results in a loss of efficiency. Because of the mass of the rotor and the rotating commutator assembly coupled thereto, greater energy and time must be consumed before the motor can reach its optimum operating speed. Consequently, the power output of the motor is reduced. In this same regard, when the motor is commutated electronically, the power-to-weight ratio is undesirably decreased and the cost of manufacture is correspondingly increased.
Accordingly, it would be desirable to reduce the mass of the rotor assembly of a DC brush type motor and commutate the motor mechanically rather than electrically so as to increase the power-to-weight ratio and efficiency of the motor by having a stationary commutator assembly with a high current capacity and a rotating brush assembly. Examples of known DC motors that have a rotating brush assembly and a stationary commutator assembly are available by referring to the following United States patents:
A DC voltage powered rotating brush motor is disclosed having a high power-to-weight ratio and a particular application for use in electric vehicles. The motor has a shaft that rotates a permanent magnet assembly relative to the field windings of the stator assembly. Coupled to the shaft are a pair of brush assemblies that rotate past a stationary double sided commutator assembly and a pair of solid, disc-like slip ring assemblies that are connected to opposite terminals of a DC voltage source.
The stationary double sided commutator assembly includes an electrically insulating support ring. Mounted on opposite sides of the support ring are first and second sets of radially extending, electrically conductive commutator bars. The commutator bars are spaced from one another by a small air gap. Opposing pairs of commutator bars at opposite sides of the a support ring are electrically connected to one another by means of a plurality of assembly screws that are pushed through respective end-to-end aligned channels that extend circumferentially around the commutator assembly and through each of the commutator bars. By virtue of the double sided arrangement of commutator bars, the current carrying capacity of the commutator assembly can be effectively doubled.
Located at each side of the stationary commutator assembly is a rotating brush assembly. The brush assemblies are electrically insulated from and aligned out of phase with one another adjacent the first and second sets of electrically conductive commutator bars. Each brush assembly includes a brush holder having three arms that project radially outward from a hub. The brush assemblies are mounted on and rotatable with the shaft of the motor by way of the hubs thereof. Flat, solid and generally triangular electrically conductive shuntless brushes are slidably received within brush cavities formed in the arms of each brush holder.
A stationary disc-like slip ring assembly is located outside each rotating brush assembly. The slip ring assemblies are biased by slip ring retention springs so as to exert a pressure against and thereby urge the brushes of the brush assemblies into constant electrical contact with the opposing first and second sets of commutator bars of the stationary double sided commutator assembly. Each slip ring assembly has an electrical terminal that projects radially from an electrically conductive slip ring body to be connected to one terminal of the DC voltage source. The slip ring terminals are electrically connected to the field windings of the motor and to the first and second set of commutator bars of the commutator assembly by means of the aforementioned plurality of assembly screws that also run through holes which extend circumferentially around the slip ring assemblies.